The present invention relates to the subscriber terminal system which includes a telephone and telemetering apparatuses. More specifically, it relates to the telemetering apparatuses which detect the signals sent from the exchange upon starting and stopping of use of the communication line between the exchange and the subscriber.
Conventionally, there have been used the telephone network, where the exchange provides with power supply to activate the telephone in house via the communication line, When an origination subscriber call up a destination subscriber, the exchange inverts the polarity of the voltage applied to the communication line between the exchange and the destination subscriber in order to notify to the destination subscriber the starting and stopping of use of the communication line therebetween.
Also, there have been the telemetering system via telephone network to easily gather information periodically. FIG. 75 is a diagram showing the telemetering system, and FIG. 76 is a block diagram showing the telemetering apparatus. In the telemetering system, for example, the electric power company, the waterworks company, and the gas company each telemeter electric power, water, and gas used in home via telephone network. In each house are installed the power telemetering apparatus, the water telemetering apparatus, and the gas telemetering apparatus corresponding to the respective companies. When one of the companies starts or stop use of the communication line for telemetering, the exchange inverts the voltage polarity of the power supply applied to the communication line between the exchange and the destination consumer. In order to distinguish a use of telemetering apparatus and a use of telephone from each other, the forms of those polarity inversions are different from each other. As the result, the telemetering apparatuses have the polarity inversion detection circuit for detecting the polarity inversion, the bell signal detection circuit for detecting the bell signal, and the controlling circuit for controlling the detection circuits and gathering data on electric power, water, and gas from the power meter, the water meter, and the gas meter.
FIG. 77 is a time chart showing wave shapes, in which FIG. 77(a) illustrates the wave shape of the polarity inversion of telephone (normal polarity inversion); FIG. 77(b) illustrates the wave shape of the polarity inversion of telemetering (slow polarity inversion); and FIG. 77(c) illustrates the wave shape of the calling bell signal. The wave shape of the bell follows only the normal voltage polarity inversion in calling the destination subscriber for telephone conversation, not following the slow voltage polarity inversion. Upon starting or stopping of use of the communication line, the telemetering apparatus tries to detect the normal polarity inversion and the calling bell signal, or the slow polarity inversion. If both of a polarity inversion and a calling bell signal are found, the telemetering apparatus does not start telemetering but the telephone does works. On the contrary, if a polarity inversion is found, but no calling bell signal is found, the telemetering apparatus starts telemetering. In summary, the conventional telemetering apparatus did not detect a slow polarity inversion owing to its technical difficulty: there has been provided no electric power during the period between the end of the first half of the slow polarity inversion and the start of the second half thereof because the applied voltage keeps ground level during the period. With respect to the above system and apparatus, there is such a document as Japanese Laid Open HEI 6-237307.
FIG. 2 illustrates a conventional polarity inversion detection circuit. The polarity inversion detection circuit has a rectifier 1 connected to a pair of communication lines L1 and L2. Moreover, the communication line L1 connects to an array of diodes 2 that are connected in series, a Zener diode 3 connected to the array of diodes in parallel, an emitter resistor 4, two transistors Darlington-connected between the resistor 4 and an output terminal of the array of diodes 2, and a polarity inversion detection amplification circuit 9 which includes a diode 7 and a resistor 8, both of which are connected in series to the collector of a transistor 6, the collector being located at the output side of the transistors 5 and 6. The communication line L2 connects to a polarity inversion detection amplification circuit 10 having the same configuration as that of polarity inversion detection amplification circuit 9. Between the output terminal of the array of the diodes 2 in the polarity inversion detection amplification circuit 9 and the output terminal of the array of the diodes in the polarity inversion detection amplification circuit 10, a Zener diode 11, a resistor 12, a capacitor 13, a resistor 14 and a Zener diode 15 are connected in series in this described order.
Between a positive electrode output terminal 1a and a negative electrode output terminal 1b of the rectifier 1, two holding circuits 16 and 17, which operate on an output from the rectifier 1, are connected in parallel. Between both of the holding circuits 16 and 17 and the negative electrode output terminal 1b, reset circuits 18 and 19 both. of which halt the operation of holding by the holding circuits 16 and 17 respectively are connected.
Upon starting and releasing use of the communication lines L1 and L2, the exchange inverts the polarity of voltage applied thereto so as to notify the telemetering apparatus of the starting and releasing. When the polarity inversion on the communication lines L1 and L2 starts and-when thereby the voltage between the communication lines L1 and L2 varies, either Zener diode 11 or Zener diode 12 detects the change to turn into a current passing state, and thus a polarity inversion detection trigger current flows in accordance with charging and discharging on the capacitor 13. The polarity inversion detection amplification circuit 9 or the polarity inversion detection amplification circuit 10 amplifies a trigger current via the array of the diodes 2, the Zener diodes 11 and 15, the resistor 12 and 14 in the polarity inversion detection amplification circuit 9 or in the polarity inversion detection amplification circuit 10. The holding circuit 16 or the holding circuit 17 holds polarity inversion information with an amplified trigger current, outputted from the polarity inversion detection amplification circuit 9 or from the polarity inversion detection amplification circuit 10, as a trigger. Also, they output the polarity inversion information to the controlling circuit using a externally attached circuit such a photo coupler. At the point of time when it is not necessary to hold the polarity inversion information, a reset signal is given from the controlling circuit so that the held information in the holding circuits 16 and 17 are cleared. Thus, they return to be in a stand-by state.
In the manner as described above, since the polarity inversion information on the communication lines L1 and L2 is obtained, conventional telemetering apparatus detects a polarity inversion using, for example, the polarity inversion detection circuit such as shown in FIG. 2. Finally, the controlling circuit determines which of telemetering or telephone the purpose of using the communication line is oriented to, which depends on a bell signal which will follow the normal polarity inversion and will not follow the slow polarity inversion.
For detection of bell signal, conventional bell signal detection circuits experience logic OR of two polarity inversion information indicating either a starting or a releasing which is generated by the Zener diodes 11 and 15 shown in FIG. 2, the resistors 12 and 14, the capacitor 13 and the polarity inversion detection amplification circuits 9 and 10, whereby, they obtain a stream of pulses like impulses and detect a bell signal based on the stream.
However, there have been the following problems (1)-(6) in the conventional polarity inversion detection circuit.
(1) Is is not possible to integrate the polarity inversion circuit in form of monolithic IC (Integrated Circuit). Because the capacitor 13, which charges and discharges for differentiation operation to generate a trigger current, requires several hundreds nF (nano farad) of capacity.
(2) Generally, the trigger the value of the trigger current depends upon the speed of the polarity inversion, or dV/dt. Accordingly, regarding high dV/dt as a proper value makes low dV/dt malfunction, while regarding low dv/dt as a proper value deteriorates the noise-proof characteristic.
(3) Some noises added on the communication lines L1 and L2 increase the voltage difference between the communication line L1 and L2 during standby to thereby cause the trigger current to flow, which causes the holding circuits 16 and 17 to malfunction as if detecting a bell signal. Returning to the standby state from such a detection state through judgment of the malfunction requires a specified period; if some noises bring a malfunction, the communication lines are not available in the period.
(4) The amount of generated trigger current changes according to the speed of the polarity inversion. Also, the amount of on-current flowing through the holding circuits 16 and 17 and the amount of ON/OFF threshold current each changes depending on the surrounding temperature. The mount of trigger current, the amount of the on-current, and the amount of ON/OFF threshold current each vary due to the respective causes. Consequently, avoiding any malfunctions requires a large margin among those currents, which obstructs realizing of low dissipation power circuit.
(5) The conventional polarity inversion detection circuit has two independent holding circuits comprising the holding circuits 16 and 17 to work in turn, which has a possibility of bringing some malfunction such as simultaneous operation.
(6) The conventional polarity inversion detection circuit has two independent holding circuits, which require the respective photo-couplers. This poses a such problem as increase in number of the parts including the above capacitor 13 employed outside.
In addition, there have been the following problems (7) and (8) in the conventional bell signal detection circuit.
(7) It is difficult to judge which of the telemetering and the telephone the purpose of using the communication line is directed to by detection of the normal polarity inversion and the slow polarity inversion.
(8) The pulse like a impulse generated upon detection of an unexpected single polarity inversion, which is not one of the normal polarity inversions for the telephone should be canceled. Because such a pulse serves to bring some malfunctions.
(9) Since the stream of pulses representing correct detection of the bell signal appears like a stream of pulses like impulses, which is hard to be processed in the other circuits.
The object of the present invention is to provide the telemetering apparatus which distinguishes the normal polarity inversion, the slow polarity inversion, and the calling bell signal applied to the communication line between the telemetering apparatus and the exchange in the telephone network.
According to one aspect of the present invention, the telemetering apparatus comprises edge detection means for detecting one of a rising edge and a falling edge characterized by each of the signals from the exchange based on predetermined levels of the edges and predetermined periods of the edges.